Method of impregnating cellulosic materials and product of said method



Patented Mar. 30, 1937 UNITED STATES 2,075,328 I rm'rnon or mascmrmc CELLULOSIO MATERIALS METHOD AND PRODUCT F SAID Gerard a. Albert, Kennett Square, Pa., asslgnor to National Vulcanized Fibre Company, Wilmington, DeL, a corporation of Delaware Application October 3, 1933, Serial No. 691,923

6 Claims. (or. 91-68) This invention relates tomethods oi impreghating cellulosic materials and tothe products of such methods.

The primary object of the invention is to provide a method of impregnating cellulosic mate-1 rials such as paper with various impregnating agents so as to impart thereto certain desirable properties such as greater water resistance without at the same time impairing other desirable 10 properties such as flexlbility'or ,pliability.

Another object is to produce an indurated fibre having a greatly decreased water absorption, but which retains substantially undiminished all the desirable qualities and characteristics usually ascribed to this type of material, particularly its flexibility or pliability.v

The method of the invention is particularly adaptable to indurated fibre of the type generally known in the art as vulcanized fibre, fibre or leatheroid. This type of materialls generally made by treating cellulosic material in the form of sheets or webs with parchmentizing or gelatinizlng agents. The cellulosic material is usually, though not necessarily, an all cotton cellulose paper. Among the various parchmentizin or gelatinizing agents that have been used or suggested. may be mentioned aqueous solutions of alkalis such as caustic soda, dilute acids such as sulphuric and nitric, metallic salts such as zincates, stannates, stannites, antimonates, alu

minates and preferably zinc chloride.

, The parchmentizing or gelatinizing agents serve to chemically hydrate, partially hydrolize',

- gelatinize or parchmentize the cellulose fibre so that when the treated material is laminated and subjected to heat and pressure, it is caused to coalesce and become indissolubly united into a homogeneous multi-ply sheet. -By leaching and "puring out the treating agent and subsequent- 40 ly drying the sheet, a hardened horn-like ma r rial'results having greatly improved characteristics as compared with the cellulosic material originally subjected to the chemical and physical treatment. Its toughness, hardness, elasticity, fiexibility or pliability, dielectric strength and the fact that it is oil-proof, impervious to organic solvents and fairly resistant to mlneralaclds render it eminently suitable as many purposes, both mechanical andelectrical. Vulcanized fibre as made by prior art methods has, howevenone serious drawback or shortcoming which greatly limits its field of, usefulness; it is far from being waterproof or impervious to water and steam. In fact, commercial. samples. of vulcanized fibre readily take up as much as.25%- or more of their weight of water depending upon a number of factors includingthe quality of raw materials and conditions under which the chemical and" physical-treatments are carried out.

Prior attempts to render vulcanized fibre'water resistant have for the most part been based upon impregnation with waterproofing materials such asyamishes, resins, oils, etc. Vulcanized fibre is, however, practically impermeable to' ordinary waterproofing materials and organic solvents which are generally used as vehicles for waterproofing materials and, hence, attempted im-. pregnation usually results in thin superficial,

coatings or films of varnishes which are not durable or water resistant and on being abraded or broken allow the absorption of high percentages of water. Likewise, it is impossible to introduce waterproofing materials into vulcanized fibre by .means of aqueous suspensions or emulsions, for vulcanized fibre is an unusually good filtering medium and merely absorbs. the water, leaving the waterproofing material as a coating.

It has been suggested in British Patent No. 316,700 to I. G. Farbenindustrie Aktiengesellshaft that the waterproofing materialsbe introduced into the fibre in the form of aqueous solutions. This patent discloses a method which depends upon the marked avidity of vulcanized fibre for water and proposes to utilize aqueous solutions of certain types or synthetic resins which can be readily converted by means of heat and pressure to a water insoluble, water resistant form. According to the disclosure of the patent the fibre is immersed in the waterproofing solu-' tion until it will take up no more resin and the saturated material is subjected to heat and pres- 7 sure. to convert the resinto final form.

Extensive tests indicate that the process results in a product which is fairly water resistant, but

which hastotally lost the flexibility or pliability so characteristic of vulcanized fibre. The product has all the physical appearance of a board made by impregnating individual sheets of paper with synthetic resins and laminating. the impregnated sheets with heat and pressure and is too brittle for the purposes for which vulcanized fibre is generally used.

The present invention depends upon the dis- 1 covery that if a substantially flexible material,

such as paper, vulcanized fibre, etc., is impregnated to substantially minimum specific gravity,

not only will it acquire the desirable properties of the. impregnating agent such as greater water resistance but it will also retain its own desirabl characteristics such as flexibility. 1

In view of the fact that'the invention is particularly well'adapted for the preparation of water resistant vulcanized fibre, this material has been selected as the illustrative embodiment of-the invention for the purpose of the present disclosure. Reierring briefly to the drawing, Figure 1 is a graph indicating the relationship between the increase in volume and'the increase in weight of a sample of fibre immersed in water at 25 C.;'

treatment as is necessary to change the water-- proofing material to its-final water resistant'form.

For the purposes of the present invention, any material may be used as the saturant or impregnating agent provided it is water-soluble at one stage and insoluble at another stage and provided further that in its insoluble stage it has pronounced waterproofing qualities. Among the ma terials fulfilling the required specifications may be mentioned the modified natural or syntheticresins falling within the following groups: 1) The water-soluble phenol-aldehyde type of resin such as is made by the Bakelite Corporation 1 deal a n Bakelite Water sndsodunderthe 9 mmn .so% Bakelite Water Soluble Resin Soluble Resin Kit-568.

I (2) The water-soluble aldehyde-ketene type of resin described in Patents" Nos. 1,502,945 and 1,761,542 to Ellis granted July 29, 1924 and June so 11, 1929, respectively.

(3) The water-soluble urea-formaldehyde and thiourea-formaldehyde types of resin such as are disclosed in Patent No. 1,507,624 to Polish et al., dated September 9, 1924 and Patent No. 1,928,788

' 85 to Novotny et al., dated Septemberlfi, loss.

(4) The water-soluble alkyd or glyptal type of resin described in Japanese Patent No. 93,029 to Habu, dated September 29, 1931 and abstracted in Chemical Abstracts, Volume 28 (1932) page 4488.

4o Thistype of resin may be made by heating gylcerol r glycol and citric or tartaric acid at 170-180 for an hour and combining the resinous. product with a fatty or aromatic acid, acetic anhydrlde, bensoic anhydrideor alkyl iodide.

*5 I prefer to employ the phenol-aldehyde type of resin, for generally speaking the phenol-aldehyde resins are the most easily convertible of all synthetic resins and for that'reason lend themselves most readily to the purposes of the present inven- 60 .tion. Bakelite Water-Soluble Rain Kit-568 is particularly suitable. This material is a watersoluble phenol-formaldehyde reaction product basically reacted. It is supplied by the manufacv turer in a water solution and maybe diluted to a 65 resinoid content of approximately 30% without signs of precipitating the resin. If greater dilution is desired, a small amount of alcohol may be added to keep the resin in solution.

An explanation of minimum specific gravity will 00 now be given. When a dry piece of 'fibre is immersed in water, it immediately takes up ,waterand beginstoswell. Aclosestudyofthis swelling with water absorption reveals the fact that the change in volume of the piece (the swell- 65 ing) is proportional to theweight of the water absorbed. This proportionality is intei'preted as meaning that the'water absorbed i into thebodyoffthe fibreisatonce takenup bythe cellulosewhich in proportion tothe amount of water taken up. As more and more water is absorbed. the cellulose becomes saturated audit can .no longer expand proportionately, with the 3 result that the linear relation between volume change and weight change ceases. Beyond this point, the'water that is absorbed into the body of v s,o7s,sse I the fibre goes to fill the-interstices of the material with consequently'a slightchange'in over-all volume of the sample; The graph of Figure 1 illustratu the foregoing explanation, the sample being a piece of granite fibrehaving a thickness of fit. Specific gravity determinations made at the same time reveal that the specific gravity of the sample decreases very rapidly at first, reaches a minimum and but gradually. The

variation of specific gravity with time of immersion is indicated on the curve of Figure 2. The

important connectionibetween the two graphs 1 thatminimumspecificgravityisthepointwhere the proportionality between volume change and weight change ceases. Physically, then, minimum specific gravity is the .where the cellulou of the fibre is saturatedand any further absorption of liquid would be putting the liquid, with its solid matter in the case of a resin solution, in the interstices of the material where itis thought to impair the desirable p operties of the fibre, particularly its flexibility or pliability.

I prefer to use a waterproofing solution conthat the concentration of the solution changes but little during the-treatment.

The fibre maybetreated-with the waterproofing solution at any desired or preferred stage in its manufacture; i. e. before or after the chemicals have been leached or pured ou or before or after the vulcanized fibre has been dried.' As a matter of fact, the process, may be applied to completed articles of vulcanized fibre. Extensive experiments indicate that, all other'thingsbeing equal, a sheet or slab of fibre treated with waterproofing material just after the chemicals have been "pured'out and while the fibre is still thoroughly wet can be rendered considerably more water resistant than an exactly similar sheet or slab of dry fibre. However, I prefer to treat dry fibre for the water of web fibre serves to change the concentration of the waterproofing solution. and renders accurate control exceedingly difilonlt.

" At the present time I'Iprefer to immerse the sheets or slabs intotanks or vesselsccntainlng the waterproofing solution until the material has absorbed suiiicient of the solution to bring its specific gravity down to the minimum. There are various ways of determining the time of immersion. A relatively simple one consists in immersing a small weighed sample of the fibre under treatment in the same waterproofing bath at the same time as the material under treatment "and determining its'specific gravity at spaced intervala' when the'sample or control has reached minimum specific gravity, it is time to remove the material from the bath; Another way is to make test runs with several samples from the batch to determine the length of time necessary to reach minimum specific gravity. By means of test runs on the different types and thicknesses of fibre produced at the plant, a series of charts or graphs-may be prepared showing the time of immersion for the different types and thicknesses. Then thevtime of immersion for any given batch may be readily determined by consulting. the appropriate chart or graph.

By immersing sheets of dry. fibre in waterproofing solutions of difl'erent concentrations, removing them at minimum specific gravity, weighing them, drying, curing and then testing them, it

solid content of .28 gram per gram of liquid, as

determined by actual test.

The test used to determine the solid contentof the liquid varnish is the standard Bakelite test.

various ways or combined with various other details without sacrificing any of its advantages.

It is to be further understood that the invention is not dependent upon any explanations or theories which have been set forth as descriptive of the actions involved, nor dependent upon the It consists in carefully weighing about 5 grams of the varnish mixture in an open dish of about three inches in diameter and then placing it in an oven at 130 C. for three hours, after which time it is cooled and weighed. The weight of the residue leftv in the dish and the weight of the liquid sample taken are used to compute the percentage of solid matter by weight. The solid matter contained in the finished water resistant fibre is computed as follows: A small piece of the fibre to be treated is first carefully weighed and then immersed in the solution with the sheets which are to be treated. At close intervals it is removed, washed in alcohol to remove the surface film', weighed in air and finally suspended in water to determine its specific gravity. Its weight at minimum specific gravity less the original weight is the'weight of the liquid absorbed. The weight of this absorbed liquid multiplied by the per cent solids of this liquid yields the number of grams of solid matter taken up by the fibre. The weight of the solids absorbed divided by the original weight is the percentage of solids contained in the sample. Since the main batch is treated in exactly the same way, it is clear that it contains the same percentage of solids.

Since the foregoing tests indicate that for a 50-50 varnish bath the fibre, if removed at minimum specific gravity, will contain about to 12% of solids by weight, a simple procedure is to remove the batch of material from the impregnating bath when it has taken upabout 10% solids. This procedure obviates the necessity for determining specific gravities.

' After the-fibre is removed from the bath it is washed in alcohol to remove the surface film, dried at 60 C. one or more days, depending upon its thickness, then pressed in a steam heated hydraulic press under a platen pressure of 200 pounds per square inch, at a temperature of 177 C. (125 pounds steam pressure) from ten to twenty minutes depending upon the thickness of the fibre being treated.

The following data is given to prove that the waterproofing treatment does not impair the desirable characteristics of vulcanized, fibrez Me" Red fibre Ho" White fibre Untreated Treated Uun'eated Treated 8, 000 10, (IX) 8, 750 9, 440 Compressive strength- 30, 100 34, 900 37, 000 39, 000

The foregoing constitutes the essential and distinctive thought of my invention. It is to be understood that its details'may be modified in ordinarily possessed by untreated paper.

soundness or accuracy of any.theoretical statements so advanced. The-invention is to be limited solely by the following claims which are to be read in the light of the foregoing description and in which I intend to claim all the novelty inherent in the invention which is permissible in view of the prior art.

In the foregong description and the following claims the term paper is to beunderstood in its ordinary significance in the art; namely, a sheet or web or cellulosic material from whatever source or sources derived and suitable for the manufacture of indurated fibre.- The terms fibre, vulcanized fibre and indurated fibre are used interchangeably to denote a cellulosic material so treated chemically and/or physically not The terms synthetic resin, resinoid and waterproofing material are used to denote a synthetic or modified natural resin or equivalent material. adapted to permeate or impregnate paper or fibre and decrease its avidity for water.

I claim:

l. A method of increasing the water-resistance of a cellulosic material without impairing its desirable characteristics, which consists in immersing said material in a solution of a synthetic resin in an intermediate stage until the combinaas to impart thereto a hardness and density tion of cellulosic material and resin reaches minimum specific gravity and converting said resin to its final stage.

2. A method of increasing the water-resistance of vulcanized fibre withoutimpairing its desirable characteristics, which consists in impregnating said fibre with a water soluble synthetic resin until the combination of fibre and resin reaches minimum specific gravity, drying the material and converting said resin to final insoluble form.

3. A method of increasing the water-resistance of vulcanized fibre without impairing its desirable characteristics, which consists in immersing said fibre in a solution of a synthetic resin in an intermediate stage until the combination of fibre and resin reaches minimum specific gravity, drying the material and converting said resin to final insoluble form.

4. A method of increasing the water-resistance of vulcanized fibre without impairing its desirable characteristics, which consists in immersing said fibre in a solution of a phenol-aldehyde resin in an intermediate stage until the combination of fibre and resin reaches minimum specific gravity, drying the material and converting said resin to final insoluble form. 5. As an article of manufacture, a sheet of substantially flexible, water-resistant material consisting of vulcanized fibre, the fibres of which are substantially saturated with a resinoid and the interstices of which are substantially devoid of resinoid.

6. As an article of manufacture, a sheet of substantially flexible, water-resistant material consisting of vulcanized fibre, the fibres of which are substantially saturated with a resinoid of the phenol-aldehyde type and the interstices of which are substantially devoid of resinoid.

GERARD A. ALBERT. 

